1. Field of the Invention
The present invention relates to a flexible display device.
2. Related Art
In the display devices, the so-called flat panel implementation having a small depth aspect ratio relatively to the area of display as represented by liquid crystal displays and plasma display panels is promoted. Thus, thin TV sets and various mobile applications have been implicated.
In addition, as for future display devices, research and development of flexible display devices which themselves are provided with flexibility to have a further degree of freedom are promoted. Owing to the use of the display device having flexibility, it is possible to improve the accommodation property by utilizing the flexibility and rounding or folding the display device when it is not used and improve the convenience at the time of transportation.
For example, it becomes possible to implement a novel sensuous analog input function by adding a pressure sensitive sensor to a flexible display device and detecting the amount of bending given to the display device by the user arbitrarily (see, for example, JP-A 2004-46792 (KOKAI)). The display device raises the convenience when the user carries it and facilitates the human interface. Thus it is considered that the display device can largely contribute to implementation of novel digital products. A key device which implements the novel digital products is a flexible display device. Liquid crystal displays and organic electroluminescence displays which are excellent in flexibility and reflection display devices called electronic paper are implemented by changing support substrates from conventional glass substrates to support substrates having excellent flexibility such as plastics. As for them, a search for optimization of the support substrate material and the structure, an array technique for matrix operation, and an electro-optic effect layer which has a higher efficiency and which can ensure reliability is being promoted at the present time, aiming to improve more flexibility.
In electronic devices, the range of flexibility in which their function can be maintained (hereafter simply referred to as flexibility range) is finite in many cases. The reason is that, for example, internal stress generated by bending brings about generation of defects and cracks which cause function breakdown in the electro-optic layer or the active matrix layer. In input devices utilizing the flexibility as well, the function range is restricted. In the user, however, the operation for the flexibility is sensuous, and the flexibility range of the display device or the display device provided with the input function is hard to intentionally control. For example, in the case where the display device is provided with a pressure sensitive sensor and the amount of bending is used as an analog input, there is a possibility that the user might give an amount of bending exceeding a limit value which can be allowed by the display device in one's eagerness to ensure a greater input value. At this time, there is a risk that the display device will not be able to withstand the amount of bending and, for example, function lowering such as display performance degradation or damage of the display device itself might be caused. Therefore, it is necessary to transmit the flexibility range of the display device to the user by using some method.
In the conventional flat panel, its plane stability is ensured by providing a member located in a peripheral part of the display device called casing with needed rigidity. However, it is not effective to the display device having flexibility, because providing the casing itself with rigidity deprives the display device itself of the flexibility.
If the casing is provided with a function of limiting the flexibility range of the display device, the casing itself becomes complicated and large-scaled. As a result, the thinness with light weight which is one of features of the flexible display device is sacrificed. In addition, the cost required to fabricate the casing is also increased. Therefore, it is desirable to form a casing having a minimum required function such as a dampproofing property, in a state in which the flexibility is more excellent so as not to give unnecessary stress to the display device.